If an infant cannot suckle it will not survive, save through extraordinary medical intervention. Primate studies to date have, by and large of necessity, been behavioral. Therefore little information exists on the mechanisms by which infants suckle or juveniles drink. Nor is it known how the vital transition from suckling to drinking and mastication occurs during normal development. Suckling mechanisms, in terms of movements of the tongue, jaws and hyoid, and patterns of muscle activity, are understood for a few nonprimate mammals. These mammals, however, are sufficiently different from primates in anatomy and adult function that the information is of little value in understanding problems of primate suckling and swallowing. If the basic questions "how do infants suckle and swallow?" and "how do juvenile drinking and mastication replace suckling?" are to be answered, there is no alternative but to conduct a well designed series of experiments on a viable and acceptable human analog. Experimental manipulation of laboratory primates is essential because a complete model of oral function must include data not readily available form information collected in a clinical situation. This study proposes a carefully controlled cineradiologic and electromyographic investigation of infant oral function in macaques as the basis for a model of normal human behavior. Data collected on the movements of tongue, hyoid and jaws, changes in shape of the tongue, and activity of craniomandibular muscles will be the basis of a biomechanical model of oral function. By quantifying how tongue movements and muscle activity change as a function of normal ontogeny, we will discover how an infant acquires, transports and swallows liquid, as well as how these functions change during growth. These experiments will provide the qualitative and quantitative data needed on nonimpaired function to facilitate future interpretations of clinical data on neonatal infants with dysfunctional oropharyngeal behavior.